Luxurious or luxuriant?

[babyignoramus]

DH and I went to a wedding last week and he told his friends it was in a lovely hotel - 'very luxuriant' - to which I said, 'don't you mean luxurious?'. He thinks the terms are interchangeable, but I don't - but I can't explain why! Pedant needed to settle the argument.

Thanks!

My Chambers Dictionary definition for luxuriant says:

'exuberant in growth; overabundant; profuse; (erroneously) luxurious.'

So there you go.

Hah! Thank you.